The effect of the methylation method on isomerization of conjugated linoleic acid (CLA) in gas chromatographic analysis was studied. Among methylation methods examined, the magnitude of isomerization of CLA was greatest with BF 3 catalyst, followed by HCl and H 2 SO 4 catalyst. Short-time methylation did not extensively change the CLA composition in all methods, and c, t and t, c isomers were essentially maintained, while the appearance of t, t isomers and unknown peaks was practically restricted. After 120 min of methylation, there was essentially no conversion in the H 2 SO 4 method, in contrast to a marked change in the BF 3 method. The antioxidants butylated hydroxytoluene, ascorbic acid, β-carotene, and α-tocopherol did not suppress conversion, while dimethylsulfoxide (DMSO) and dimethylformamide (DMF) attenuated the changes in CLA composition. Suppression was more effective in the H 2 SO 4 method than in the BF 3 method. Thus, methylation with H 2 SO 4 in the presence of a proper amount of DMSO or DMF is recommended for esterification of CLA.
|Number of pages||6|
|Journal||JAOCS, Journal of the American Oil Chemists' Society|
|Publication status||Published - 1999 Jan 1|
ASJC Scopus subject areas
- Chemical Engineering(all)
- Organic Chemistry